I've found a headband cushion that does a pretty good job of preventing the APM's two hard plastic-covered metal bars from digging into my scalp, due to the APM's stretchy headband fabric flattening out over the past year and a half. They're the Geekria Hook and Loop Headband Cover + Headband Pad Set:
https://www.amazon.com/gp/product/B08HQGTR7D. It's currently $15.99. For some reason the listing says this is a frequently returned item, but I've had no issues with it, and it seems sturdy. It also works with a slew of other headphone models, which the listing lists. The pad part of the assembly is separately replaceable, since it's held to the zippered cover using Velcro, and Geekria also has some kind of cooling pad option as well.
I also bought two other manufacturer's headband covers that look sort of similar to the Geekria in their listing photos, to compare them all, one from TXEsign and another from Desing Wish (who comes up with these names?), but the padding in those models is almost nonexistent.
I also bought a pair of third-party APM ear cushions from Gvoears, for a little less than half the price ($28) of Apple's ($70), since my APM's original ear cushions had flattened out slightly and so I feel more pressure around my ears from them, but I'm not sure how impressed I am with the Gvoears cushions since they don't seem to provide as much cushioning as the original cushions did--they cushion only a little better than my original cushions do now, so I didn't come out ahead much.